Early Eocene London Clay deposits at High Ongar, Essex (Part 2)

Bob Williams (UK) In the previous part of this article (see Early Eocene London Clay deposits at High Ongar, Essex (Part 2)), I located the beds exposed at High Ongar in Essex (TQ 556809) within the general, stratigraphic framework of the London Clay. I also argued that examining the habitats in which families of crustacea live today provides clues about the sort of habitats that may have existed when the London Clay in the pits at Aveley in Essex and Ongar (TL 562024) was deposited. In this part, I will continue this comparison using modern lobsters, shrimps and other animals to provide clues about the habitats that may have existed at Ongar and at various other London Clay sites when their fossil relatives were alive. I will also show how one can locate a site like Ongar within the stratigraphic column. Fig. 1. Estimated position of the clay exposures at High Ongar Essex and nearby Aveley, showing the London Clay sedimentary deposits. At this point, it is worth bearing in mind the conditions in which the London Clay deposits are believed to have been laid down. London Clay is not one, uniform deposit. There are a number of sedimentary horizons within the deposit, each horizon reflecting the environment in which it was formed. Broadly, the London Clay is thought to have been laid down in a marine environment influenced by a tropical or subtropical climate. Water depth is thought to have averaged about 200m, but would obviously have varied locally. … Read More

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